Description: (Applicant's abstract) Once a target location has been identified for a drug, protein or gene, proper spatial and temporal control in the delivery of these molecules is a fundamental problem in biomedical engineering. In one promising approach for anticancer drugs called antibody-directed enzyme prodrug therapy (ADEPT), a monoclonal antibody (MAb)-enzyme conjugate selectively binds an antigen expressed on tumor cells, and the enzyme moiety releases drug from the subsequently injected prodrug at the target site. ADEPT is in clinical trials. However, drawbacks of MAb-enzyme conjugates limit ADEPT. They express low chemical and physical stability, short blood-half life, immunogenicity and low tumor to blood ratio. Attaching a common water-soluble polymer, methoxy-terminated poly(ethylene glycol) (PEG), onto MAb-enzyme conjugates enhances stability, prolongs blood circulation and reduces immunogenicity, but with no marked increase in tumor to blood ratio. Our research will focus on biospecific polymer-enzyme conjugates and their role in ADEPT. We attached a biotinylated PEG on a model enzyme, carboxypeptidase A (CPA). A biotin moiety at a chain end of PEG may mediate several useful functions for the first time for a PEG-enzyme conjugate. A biotin moiety may mediate the separation of PEG-CPA conjugate by affinity chromatography, fractionating in terms of number of attached biotinylated PEG on CPA using an immobilized monomeric avidin. A biotin moiety may tether an antibody in conjunction with biotin and streptavidin. Lastly, a biotin moiety may bind a clearing agent (e.g., streptavidin) in blood, an interaction that may mediate the clearance of biotinylated PEG-CPA conjugate by the liver and an increase in its tumor to blood ratio. The specific aims of the proposal: (1) To prepare a biotinylated PEG-CPA conjugate with controlled levels of biotinylated PEG at varied molecular weight by reductive amination and by affinity chromatography with immobilized monomeric avidin. (2) To study the catalytic activity and the stability of fractionated biotinylated PEG-CPA conjugates. (3) To study the immunogenicity and the plasma profile of fractionated biotinylated PEG-CPA conjugates in mice, focusing on their clearance by streptavidin. (4) To tether an IgG1 (174H.64) together with biotin and streptavidin on biotinylated PEG-CPA conjugate with optimized properties, purify the conjugate to obtain a 1:1 complex, study its stability, and assess target cell binding in vitro. (5) To study the plasma profile and the biodistribution of antibody-biotinylated PEG-CPA conjugates ("active" targeting) and biotinylated PEG-CPA conjugates ("passive" targeting) in tumor-bearing mice (KLN-205), assessing the effect of injected streptavidin.